The present invention relates to an apparatus for inspecting a printed circuit board using laser beam. More particularly, this invention relaters to an apparatus for detecting unremoved material remaining in the bottom of blind via hole or processed groove provided in a laminated printed wiring board, or measuring the thickness, optically, using laser beam.
Along with the recent advancement in performance of electronic appliances, higher density of wiring is being demanded. To satisfy this demand, the printed circuit board is laminated in multiple layers and down-sized.
A laminated printed wiring board requires formation of ultra-fine stop holes for conduction and connection between layers. These holes have a diameter of about 150 xcexcm and are called blind via hole (BVH). With present day technology, it is difficult to drill holes or process stop holes of xc3x80.2 mm or less. Furthermore, the thickness of the insulating layer is generally less than 100 xcexcm in a high density printed circuit board, and depth control is difficult in such thin layer. accordingly, it is impossible to form ultra-fine BVH by drilling.
A method using laser beam is being noticed as a BVH forming method replacing the drilling process. This processing method makes use of the difference in the absorption of light energy in the insulating material for forming the printed circuit board such as resin and glass fiber, and in the conductive layer which is made of copper.
As the light source of laser beam, carbon dioxide laser is partly put in use, because, copper reflects carbon dioxide laser almost completely. As shown in FIG. 22(a), a copper foil removal part b of desired diameter is formed at a specified position of copper foil a by etching or the like. Then, and by irradiating this copper foil removal part b with laser beam L, the insulating substrate part c of resin or glass fiber is decomposed and removed. Thus, an ultra-fine hole d is formed as shown in FIG. 22(b).
As shown in FIG. 23, moreover, a copper foil e may be previously laminated inside of the hole processing part (inside of the insulating substrate). Accordingly, decomposition and removal of the insulating member stops at this copper foil e, so that a stop hole f stopping securely at the copper foil e can be formed.
However, as shown in FIG. 23, if the stop hole f stopping at the copper foil e is machined using carbon dioxide laser, even if the laser beam is sufficiently emitted, the resin of the insulating member of thickness of 1 xcexcm or less is left over on the copper foil e. This remaining resin after must be removed completely in a later process by etching with permanganic acid or the like.
Some times these holes are very small in diameter. Therefore, the etchant hardly goes inside the hole. If the thickness of the residual resin exceeds 1 xcexcm due to defective laser machining condition or the like, then the residual resin may not be removed completely in some holes. If the BVH is formed by plating in this state, the resin is partly remaining between the plating film and the inner layer copper foil, and if stress is applied by heat cycle or the like, the plating film may be peeled off from the portion of the residual resin. Accordingly, it is required to inspect the thickness of the residual resin of the stop hole after laser machining.
As an apparatus for such inspection, an optical microscope as shown in FIG. 24 is used. In this inspection apparatus, white light from a light source 100 is emitted to a printed circuit board W through an objective lens 102 from a beam splitter 101. The light reflected from the printed circuit board W is magnified by the objective lens 102, and an inverted real image Ea is formed ahead of a focusing lens 103, and its real image Eb is taken by a CCD camera 104.
When the white light is emitted to the surface of the residual resin, it is partly reflected, but the rest passes through the residual resin to reach the copper foil in the bottom. This light that falls on the copper layer is reflected therefrom. Therefore, when white light is emitted to the thin resin layer on the copper foil as illuminating light, the majority of reflected light returns from the copper foil. Thus, it is hard to discriminate the presence of residual resin.
Accordingly, in the inspection apparatus using optical microscope, although a residual resin of more than 10 xcexcm may be detected, the precision of detection is poor as for residual resin of about several xcexcm. Thus, this apparatus is not suited to inspection in mass production line, but can only be used to inspect the thickness of the residual resin after cutting and grinding the processing part after plating and observing the section. Further, this apparatus takes too much time in inspection, and all pieces cannot be inspected.
An optical inspection apparatus that uses ultraviolet laser beam is disclosed in Japanese Patent Application Laid-Open No. 7-83841. This optical inspection apparatus comprises, as shown in FIG. 25, an ultraviolet laser source 200, a collimator lens 201, a mirror 202, a beam splitter 203, a motor-driven rotating polyhedral mirror 204, a scan lens 205, a re-focusing lens 206, a pin hole member 207, and a photomultiplier 208.
In this optical inspection apparatus, the laser beam generated by the ultraviolet laser source is magnified by the collimator lens 201, the magnified laser beam is guided into the rotating polyhedral mirror 46 by way of the mirror 202 and beam splitter 203, and it is scanned by the rotating scanning mirror 46 and focused on the printed circuit board W to be inspected by the scan lens 205.
The ultraviolet ray generated from the printed circuit board W by irradiation with laser beam is returned recursively in the reverse route of the incident route, and is guided into the retroreflection detecting system by the beam splitter 203 disposed in the optical path. This ultraviolet reflected light is focused by the re-focusing lens 206. On the focusing plane of the re-focusing lens 206, the image near the irradiation point of the laser beam of the printed circuit board W to be inspected is observed. By the pin hole member 207 disposed on this focusing plane, only the central part is separated, and detected by the photomultiplier 208.
This optical inspection apparatus inspects by scanning over the entire printed circuit board to detect the stop holes and grooves. Accordingly, it takes time. This problem arises because the rotating polyhedral mirror is used, and the laser beam cannot be brought up to the commanded position.
Besides, because the inspection makes use of the reflected light, the inspection result may vary depending on the inclination of the printed circuit board to be inspected. Furthermore, since the reflected light is detected by disposing a mask (pin hole member) on the focusing plane and extracting the light in its central part, the luminance is too low and reliable detection of residual resin is difficult.
The invention is devised to solve these problems, and it is hence an object thereof to present an apparatus for inspecting a printed circuit board of high reliability capable of detecting the residual resin on a copper foil nondestructively, securely, and at high precision and high speed, and moreover an inspection apparatus of printed circuit board having a re-processing function for re-removing the unremoved material.
The invention presents an apparatus for inspecting printed circuit board. This apparatus comprises a laser oscillator, a scanning device for positioning the irradiation position of laser beam emitted from the laser oscillator to a position of arbitrary coordinates in the mutually orthogonal X-axis direction and Y-axis direction being commanded, and a detector for detecting the light generated from the printed circuit board irradiated with the laser beam.
Therefore, the position of arbitrary coordinates commanding the irradiation position of laser beam can be instantly set by the scanning device.
Further, in this inspection apparatus, the scanning device is composed by combination of two galvanomirrors having mutually orthogonal rotary shafts, and a scan lens.
Therefore, the irradiation position of laser beam is set at high precision by the combination of two galvanomirrors and scan lens.
Further, this inspection apparatus further comprises a controller for storing the position of coordinates for processing stop hole or groove in the printed circuit board, and controlling the irradiation position of the laser beam at the stored position of coordinates by the scanning device, and a judging unit for judging approval or rejection of the inspection result at each position of coordinates on the basis of the output of the detector.
Therefore, the irradiation position of laser beam by the scanning device depending on the stored position of coordinates is controlled by the controller. The judging unit judges approval or rejection at each position of coordinates on the basis of the output signal of the detector.
Further, this inspection apparatus further comprises a focusing unit for focusing the laser beam emitted from the laser oscillator, and an image transfer optical system and a mask member disposed between the laser oscillator and the focusing unit.
Therefore, the laser beam can be emitted to the printed circuit board in a beam shape of a same shape as the hole shape of the mask member such as perfect circle.
Further, in this inspection apparatus, the beam diameter of the laser beam emitted to the printed circuit board to be inspected is set smaller than the diameter of stop hole or width of the groove.
Therefore, even if there is a slight positioning error, the laser beam will not go out of the stop hole or the groove, and accurate inspection is possible.
Further, in this inspection apparatus, approval or rejection is judged by emitting a spot of laser beam to a plurality of positions of one stop hole or the groove to be inspected.
Therefore, a laser beam spot is emitted to the plurality of positions for one stop hole, so that an accurate inspection is realized.
Further, in this inspection apparatus, approval or rejection is judged by scanning the stop hole or the groove in a cross form.
Therefore, approval or rejection can be judged without scanning the entire stop hole or the groove.
Further, in this inspection apparatus, the detector has optical elements disposed in an array, and is designed to issue signals from each optical element.
Therefore, approval or rejection can be judged by the detector on the image of the reflected light from the printed circuit board to be inspected.
Further, this inspection apparatus further comprises a camera, and a spectroscope disposed on the way of an optical path of reflected light from the printed board for separating the reflected light from the printed circuit board into the detector and camera.
Therefore, approval or rejection can be judged by the camera on the image of the reflected light from the printed circuit board to be inspected.
Further, this inspection apparatus further comprises a light shielding unit for selectively shielding the propagation of the laser beam emitted from the laser oscillator and the reflected light from the printed circuit board.
Therefore, it avoids unexpected emission of laser beam to the printed circuit board, or input of the reflected light from the printed circuit board into the laser oscillator side.
Further, in this inspection apparatus, the criterion is set on the basis of the light intensity of the resin part of the printed circuit board to be inspected actually measured before start of inspection, and the light intensity of normal hole.
Therefore, approval or rejection is judged accurately regardless of the type of the resin part of the printed circuit board or lowering of intensity of laser beam.
Further, in this inspection apparatus, trouble of the laser oscillator or the like is self-diagnosed on the basis of the light intensity of the printed circuit board to be inspected actually measured before start of inspection.
Therefore, trouble of the laser oscillator or the like is self-diagnosed before start of inspection by the light intensity of the printed circuit board to be inspected.
Further, this inspection apparatus further comprises a laser detector for detecting the intensity of the laser beam emitted from the laser oscillator, in which approval or rejection is judged by the output signal of the detector and output signal of the laser detector.
Therefore, approval or rejection can be judged correctly regardless of lowering of intensity of laser beam or the like.
Further, in this inspection apparatus, a test piece is fixed at a specified position, and a laser beam is emitted to the test piece to detect the irradiation position, and thereby the error of the optical system is corrected.
Therefore, the error of the optical system can be corrected automatically.
Further, this inspection apparatus further comprises a temperature detecting unit and a humidity detecting unit, in which the error of the optical system is corrected when the temperature detected by the temperature detecting unit or the humidity detected by the humidity detecting unit is changed more than a specified value.
Therefore, the error of the optical system is corrected automatically when the temperature or humidity is changed more than specified.
Further, in this inspection apparatus, the error of the optical system is corrected periodically at every specified interval.
Therefore, the error of the optical system is corrected automatically upon every lapse of specified time.
Further, this inspection apparatus further comprises a laser oscillator for re-processing, and a laser optical path selector for emitting the laser beam of the laser oscillator for re-processing selectively to the printed circuit board with the same optical axis as the laser beam of the laser oscillator for inspection, in which the defective part is corrected by emitting the laser beam of the laser oscillator for reprocessing to the processing part of the stop hole or the like judged to be defective.
Therefore, the defective part can be corrected accurately on the inspection apparatus.
Further, in this inspection apparatus, the position of coordinates at the location of a defective part is stored, and the defective part is processed after inspection of one printed circuit board.
Therefore, the defective part can be corrected accurately and efficiently on the inspection apparatus.
Further, this inspection apparatus further comprises a collimation mechanism for changing the beam diameter of the laser beam emitted from the laser oscillator, in which the defective part is corrected by emitting a laser beam of a beam diameter reduced from that of inspection by the collimation mechanism, to the processing part of the stop hole or the like judged to be defective.
Therefore, the defective part can be corrected accurately on the inspection apparatus without requiring the laser oscillator for re-processing.
Further, in this inspection apparatus, the defective part is processed, starting from a carbide area near the defective part.
Therefore, the defective part can be corrected accurately on the inspection apparatus without reducing the beam radius so precisely.
Further, in this inspection apparatus, a processing substrate for correction is processed, and the error of the optical system is corrected by detecting this processing position.
Therefore, by processing the processing board for correction, the error of the optical system can be corrected by detecting this processing position.
Further, in this inspection apparatus, an annular or cross shape is processed, and the error of the optical system is corrected by detecting this processing position.
Therefore, if the aperture of the processed hole is small, the error of the optical system can be corrected by detecting this processing position.